With the advent of the privately owned home telephone, and the high expense of service calls, wherein a repairman must personally visit the dwelling or other installation where the telephone is located, a need has arisen for diagnostic telephone test instruments which can be kept at service facilities and to which the telephone owner may bring his telephone for diagnostic testing. Current commercially available telephone equipment testers used at such service facilities commonly test the basic operability of the telephones and cords therefor, but not telephone answering equipment, and are generally very expensive pieces of equipment.
In addition to a desirable low cost objective, such equipment should be as simple as possible for untrained personnel to use and should have the capability of testing the principal functions carried out by both telephone handset and telephone answering equipment. To the applicant's knowledge, all currently existing telephone equipment testers fail to satisfy one or more of these objectives.
For example there remains a need for an inexpensive means for testing the accuracy of the dialing system, both pulse dialing and tone dialing. One current approach is embodied in the Teltone M-501 telephone tester manufactured by Teltone Corporation, Kirkland, Washington. In this unit, upon dialing a given digit, a replica of the digit dialed is presented as a visual display in a single-digit readout display unit configured in the form of a well-known light-emitting diode digital display unit. If the digit displayed does not correspond to the digit dialed, the tester knows that the dialing system is malfunctioning.
Such a system is inexpensive and functions quite adequately in the testing of a manual pulse or time dialing system; however, it cannot test the operation of an automatic dialing telephones which have frequently dialed numbers stored in memory therein. The memory sections of these telephones produce high speed pulse readout representing the chosen stored telephone number, and the single digit display portions of this tester cannot properly respond to the multi-digit readout pulses of these telephones since the user is unable to distinguish the digits on the display because the user sees nothing but a high speed flickering of the display during such a test. One expensive solution to this problem has been the use of a multi-digit display incorporated in telephone test equipment Model No. PAL-1 made by Conway Engineering Inc., of Oakland, Calif. This unit employs a microprocessor-based multi-digit storage and readout system wherein the entire dialed telephone number appears as a serial string in a multi-digit display element capable of accommodating up to 16 digits. However, there remains a need for an inexpensive one digit display tester which can test the high speed dialing capability of these automatic dialing telephones.
Because those telephones communicating with a given central office may be connected to telephone lines of lengths of up to 10 miles, the effective line length being determined by the proximity of the telephone to the central office, the bell ringing system of telephones must be adequately responsive over a wide range of possible line impedances between the telephone and the central office. To cope with this and related problems, telephones are designed to ring on all signals above a certain minimum level (40 volts r.m.s. typically), but not below this level. Defective telephones sometimes will not respond to this minimum level, and so will not operate properly at the maximum distance from the central office. Neither of the above mentioned telephone testers provides a way of determining whether the bell circuit of the suspect telephone is capable of ringing at the minimum level.
During the initial introduction of tone-dialing telephones, the polarity of the DC voltage locally applied to such telephones via the in-house telephone cabling was deliberately reversed so that tone-dialing telephones would not operate. As a result, many of these wiring installations today provide an improper polarity at the wall plug into which polarity responsive telephones are to be plugged. To avoid this problem electronic tonedialing telephones are now manufactured with a bridge circuit consisting of four steering diodes to accommodate either polarity of DC voltage applied thereto, so that such telephones may be connected to lines of either polarity. As will subsequently be discussed in detail, failure of these steering diodes can cause the given telephone to function on a line of one polarity, but not the other, with the result that the user finds that his telephone will function properly when plugged into some wall outlets, but will be totally inoperative when connected to others. Inexpensive telephone testing equipment useful at publically available service facilities to providing a rapid test for steering diode failure has not been heretofore available.
In the manufacture of the 4-wire telephone cords having keyed connector plugs at either end, and configured to connect between the telephone handset and the telephone base, and from the telephone base to the telephone wall outlet, occasionally one end connector will be miswired by the manufacturer, i.e. the wiring at one connector will be completely reversed. Although both of the above referenced telephone testers have provision for testing short and opencircuits in such cords, neither provides provision for detecting such reversal. This constitutes a serious drawback, since a reversed cord may readily pass conventional short- and open-circuit tests, and yet be completely non-functional. Moreover, both of the above referenced testers require a rather complex interpretation of multi-light open and shortcircuit indicators, which can be a source of confusion to users who either do not have adequate training, or who use the tester only infrequently. Thus, there is a need for a simple, easily interpreted cord tester which will have the capability of detecting such wiring reversals.
Finally, there is a need for a test system which will test not only telephones, but which will also test for proper operation of automatic telephone answering systems. Such systems are designed to automatically come on line after a prescribed ringing interval, produce a recorded message in a playback mode, thereupon actuate to a recording mode for accepting messages, and then revert to the dormant waiting state. To the applicant's knowledge, there is no system currently available which adequately emulates signal conditions applied to such automatic answering services to allow a thorough and easily conducted test thereof.